1. Field of the Invention
The present invention relates to terminals and other apparatus attached to data processing systems and more particularly to protocols used for communicating between a terminal and a data processing system.
2. Description of the Prior Art
Digital data processing systems are frequently connected to data input or display devices by means of asynchronous links over which data is transmitted as a series of sequential codes. Communication between the input or display device and the digital data processing system is achieved by means of protocols, sequences of codes to which the devices or the data processing system respond in a predetermined fashion. Prior-art protocols have defined rather simple operations, for example, the display of a character or the movement of the cursor. While such operations did serve their purpose, some desirable operations could not be specified and others could be carried out only by means of a long and complex series of protocols.
As interactive computing has become popular, the need for more powerful protocols has become apparent. Such protocols increase the productivity of programmers by decreasing the complexity of dealing with terminals, and they increase the efficiency of systems using them by decreasing the number of protocols which must be sent between the data processing system and the input or display device.